It is well known to provide liquid fabric conditioning compositions which soften in the rinse cycle.
Such compositions comprise less than 7.5% by weight of softening active, in which case the composition is defined as “dilute”, from 7.5% to about 30% by weight of active in which case the compositions are defined as “concentrated” or more than about 30% by weight of active, in which case the composition is defined as “super-concentrated”.
In many markets around the world, it remains highly desirable to provide dilute fabric conditioning compositions since many consumer express a preference for dilute compositions over semi-dilute, concentrated and super-concentrated compositions. Such preferences include a more pleasing rheology and also because there is less chance of overdosing a dilute composition whereas it is much easier to accidentally overdose a concentrated composition.
Furthermore, dilute compositions can be advantageous to the manufacturer because the high levels of water present relative to the level of water in a concentrated composition makes the dilute composition easier to disperse in the rinse liquor without requiring additional expensive dispersion agents. Other advantages of dilute compositions over concentrated compositions include greater stability upon storage due to the greater dilution of destabilising components such as perfumes.
In traditional fabric conditioning compositions, non-ester-linked quaternary ammonium fabric softening agents have been used although there is a trend away from such compounds to ester-linked quaternary ammonium fabric softening agents.
It is desirable to use ester-linked compounds due to their inherent biodegradability.
Such ester-linked quaternary ammonium compounds contain hydrocarbyl chains which can be unsaturated, partially hardened or fully saturated.
It is particularly desirable to use substantially fully saturated quaternary ammonium fabric softening compounds due to their excellent softening capabilities and because they are more stable to oxidative degradation (which can lead to malodour generation) than partially saturated or fully unsaturated quaternary ammonium softening compounds.
Of the types of ester-linked quaternary ammonium materials known, it is desirable to use those based on triethanolamine which produce at least some mono-ester linked component and at least some tri-ester linked component since the raw material has a low melting temperature which enables the manufacturing process of the composition to occur at low temperatures. This reduces difficulties associated with high temperature handling, transport and processing of the raw material and compositions produced therefrom.
However, a problem identified with dilute fabric conditioning compositions is their apparently inferior softening performance compared to a concentrated version of the same composition. Without being bound by theory it is believed that this stems from the poorer molecular packing of the quaternary ammonium softening material in the lamellar phase of the composition when water content is high.
An additional problem associated with softening composition comprising quaternary ammonium softening materials based on triethanolamine (i.e. having a mixture of mono-, di- and tri-ester quaternary ammonium species) is their inferior softening performance, independent of their concentration, compared to those quaternary ammonium softening materials containing predominantly di-ester quaternary ammonium species.